In recent years, fuel cell cogeneration systems which can supply both heat and electricity are being developed from the viewpoint of preservation of the global environment. In such a system, a hydrocarbon fuel such as natural gas is reformed with steam to produce hydrogen-rich reformate (reformed gas) in a reforming device, and the produced reformate is supplied to a fuel cell to generate electricity. Therefore, the reforming device is an important element to be developed for the economic efficiency and energy efficiency of the entire system.
In general, when the fuel cell is a phosphoric acid fuel cell, the reforming device has a combustion section for supplying reforming heat, a reforming section in which a hydrocarbon is reformed into hydrogen and CO by a reforming reaction with steam, and a shift converter section in which CO in the reformate is shift-converted into hydrogen and CO2 by a shift converter reaction with steam. When the fuel cell is a solid macromolecule fuel cell, the reforming device has a combustion section for supplying reforming heat, a reforming section, a shift converter section, and a selective oxidation section in which residual CO in the CO shift-converted gas is removed by a selective oxidation reaction with oxygen. For the purposes of making a reforming device compact and improving the thermal efficiency of a reforming device, an integrated reformer in which all components are integrated is proposed. For example, a multiple-cylinder type reformer and a stacked plate type reformer have been disclosed.
However, in conventional multiple-cylinder type reformers, a burner combustion section with a high-temperature, a reforming section which needs to be heated to continue a high-temperature endothermic reaction therein, and a shift converter section and a selective oxidation section which need to be cooled to continue medium-low-temperature exothermic reaction therein are arranged in concentric cylinders. Thus, the conventional multiple-cylinder type reformers have a problem that the structure is considerably complicated and a high manufacturing cost is required. Also in conventional multiple-cylinder type reformers, since the cylindrical partitions for dividing the sections have large lengths and areas and since the differences in temperature between the sections are large, a large thermal stress is generated at the joints between the sections and a considerable amount of heat passes through the partitions. As a result, the temperature distributions in different sections affect each other, making the control of the temperatures difficult and making the start-up time longer. Conventional stacked plate type reformers have basically the same problems as multiple-cylinder type reformers.
In addition, conventional reforming devices can process only either gas fuels such as city gas and natural gas or liquid fuels such as gasoline, kerosene and methanol. To use a gas fuel, mechanisms for preheating the gas fuel and for mixing the gas fuel with steam are required. To use a liquid fuel, a mechanism for evaporating the liquid fuel is required. Therefore, both reforming devices for gas fuels and reforming devices for liquid fuels are conventionally prepared to satisfy the demands of users.
However, gas fuels and liquid fuels are supplied from different suppliers and treated differently in terms of taxation such as gasoline excise taxes. Accordingly, when the reforming devices can process both gas fuels and liquid fuels, the users of fuel cells can have an advantage that they can use the best fuel depending on the prevailing economic situation. In addition, when reforming devices which can process both gas fuels and liquid fuels are manufactured, the manufacturing cost may be reduced by mass production as compared with when reforming devices for gas fuels and reforming devices for liquid fuels are manufactured separately.
The present invention has been made to solve the above problems. It is, therefore, a first object of the present invention to provide a fuel reformer which is relatively simple in structure and can be manufactured at a low cost. A second object of the present invention is to provide a fuel reformer which generates little thermal stress and has excellent durability. A third object of the present invention is to provide a fuel reformer in which the control for optimum temperature distribution is easy in every parts and which has high thermal efficiency and a short start-up time. A fourth object of the present invention is to provide a fuel reformer which can reform both gas fuels and liquid fuels.